Pumpable seat assembly and use for well completion

ABSTRACT

An assembly and process for fracturing, stimulating and producing a wellbore having a plurality of oil or gas producing zones is provided comprising introducing into the well the pumpable seat assembly comprising a generally cylindrical tube having an outer diameter and an inner diameter with an upper end forming a ball seat; setting the pumpable seat assembly below an oil or gas producing zone to be produced; introducing a dissolvable ball into the well, said dissolvable ball having a sufficiently large enough outer circumference so that it can sit on the ball seat and temporarily restrict a flow of fluids to the portion of the wellbore located below the pumpable seat assembly; and fracturing the oil and gas producing zone to stimulate oil or gas production; whereby the biodegradable ball is configured to dissolve within a predetermined period of time so that when it dissolves any oil or gas produced from zones below the pumpable seat assembly can flow through the cylindrical tube.

FIELD OF THE INVENTION

The present invention relates generally to the field of vertical andhorizontal well completion, and, more particularly, to a process forfracturing, stimulating and producing a wellbore without having to millout and remove fracturing/bridge plugs and to a pumpable seat assemblyfor use with said process.

BACKGROUND OF THE INVENTION

Oil and gas well are drilled to a depth in order to intersect a seriesof formations or zones which produce hydrocarbons. Often the drilledwells are cased with steel casing pipe and cemented to secure the casingin place. Hence, it is necessary to create a flow path from these casedproducing zones to the surface of the wellbore. This is generallyaccomplished by stimulation processes such as fracturing using water,various chemicals and/or proppants. However, the steel and cementbarrier needs to be first perforated with shaped explosive charges priorto fracturing the surrounding oil or gas reservoir.

Depending on the number of producing zones in a particular reservoir,usually several elevation levels and/or lateral intervals will need tobe fractured. Thus, it is common in the industry to use a temporary wellcompletion plug which is generally set in the bore of the steel wellcasing with a setting tool just below the level or interval where theperforation of the steel and cement barrier and fracturing occurs. It isunderstood that these bridge or “frac plugs” can also be pumped down thewell on an electric wireline, either by itself or in combination withthe perforating gun assemblies. When the barrier is perforated, “fracfluids” and/or sand are pumped down to the perforations and into thereservoir to stimulate movement of the oil or gas. Use of the temporaryplug prevents contamination of the already fractured levels below.

Interval isolation and fracturing or stimulation can be performed onboth vertical and horizontal wells with multiple planned intervals,often with multiple intervals and sometimes greater than 25 intervalsper well at varying depths including sometimes greater than 6000 MetersBelow Kelly Bushing (MKB). Bridge/frac plug technology for intervalisolation for frac stimulation purposes is proven, effective,predictable and repeatable.

Unfortunately, once all of the zones have been stimulated, thesetemporary plugs may prevent the flow of oil or gas to the surface. Thus,traditionally, these plugs need to be milled or drilled out using adrill bit using jointed pipe or coiled tubing. However, there areoperational risks associated with this process and, further, this is atime consuming and costly procedure. Furthermore, it has been found thatfrac plugs having even a minimal amount of steel are difficult to drillduring removal and can damage the drill bit.

Coil tubing or jointed pipe intervention to mill out and remove theplugs on extended reach wells, e.g. lateral length exceeding 2500 m, isextremely costly, unpredictable and sometimes impossible due to metal tometal friction encountered sliding in the casing, creating what is knownas coil tubing lock-up. In some cases, frac plugs that are not reachabledue to friction lock up issues are left in the well (i.e., not milledout) and intervals left behind these frac plugs are expected to flowthrough a ¾ inch hole in the center of the frac plugs. Flow cansometimes be restricted by the number of frac plugs which were notaccessible for mill-out due to the friction lock encountered. In somecases operations are exposed to such risks as sticking the coil tubingor bottom-hole assembly (BHA) in the well, resulting in fishingoperations for pipe recovery. Fishing operations can cost an operatingcompany millions of dollars depending on difficulty and risk, in extremecases wellbore have been lost due to fishing operations and associatedcosts.

Accordingly, there is a need in the art for a well completion processand plug which will allow the plug to behave like a frac plug for atemporary period of time and then allow the flow of gas and or oil fromthe reservoir up to the well head without the need for drilling the plugout.

SUMMARY OF THE INVENTION

The present invention relates generally to a process and apparatus formultiple interval isolation of a horizontal or vertical well, whereintervention such as drilling out frac plugs is not necessary for wellcompletions. Generally, a frac plug is provided, which is a seat andslip assembly that would be applicable to more than 80% of vertical andhorizontal completions activity within the industry and that can beconfigured to fit all casing sizes and casing weights. In oneembodiment, the pumpable seat assembly would be deployed or pumped onelectric wireline down the well by itself or in combination with theperforating guns to a desired depth within the well. A standard settingtool would set the pumpable seat assembly in the casing and the wirelinewould then log on depth the guns and perforate the interval at desireddepth and pull to surface.

In one aspect, a dissolvable ball is supplied which would be dropped bythe service provider into the well from surface and then pumped downholeuntil the dissolvable ball lands on the pumpable seat assembly andprovides isolation from the previous interval for frac stimulationpurposes. The process can then be repeated a multiple number of times inthe same wellbore using additional pumpable seat assemblies anddissolvable balls. Once the frac or stimulation services are completed,the dissolvable ball will dissolve and the well can be flowed onproduction, or equipped with production tubing, all without any wellboreintervention.

In one aspect, the pumpable seat assembly has an inner diameter that isgreater than about 1 inch. In one embodiment, the assembly has an innerdiameter of about 2 inches and larger. By having a larger inner diameterthan conventional frac plugs, once the dissolvable ball has dissolved,the flow would not be restricted.

In one aspect, the invention comprises a process for fracturing,stimulating and producing a wellbore having a plurality of oil or gasproducing zones, comprising:

-   -   introducing into the well a pumpable seat assembly comprising a        generally cylindrical tube having an outer diameter and an inner        diameter with an upper end forming a ball seat;    -   setting the pumpable seat assembly below an oil or gas producing        zone to be produced;    -   introducing a dissolvable ball into the well, said dissolvable        ball having a sufficiently large enough outer circumference so        that it can sit on the ball seat and temporarily restrict a flow        of fluids to the portion of the wellbore located below the        pumpable seat assembly;    -   fracturing the oil and gas producing zone to stimulate oil or        gas production;        whereby the biodegradable ball is configured to dissolve within        a predetermined period of time so that when it dissolves any oil        or gas produced from zones below the pumpable seat assembly can        flow through the cylindrical tube.

In one embodiment, the inner diameter of the cylindrical tube issufficient to allow relatively unrestricted flow of oil or gas therethrough. In one embodiment, the inner diameter is greater than about 1inch. In one embodiment, the inner diameter is about 2 inches andlarger.

In another aspect, the pumpable seat assembly is provided fortemporarily sealing a well casing, the pumpable seat assemblycomprising:

-   -   a generally cylindrical tube having an outer diameter and an        inner diameter with an upper end forming a ball seat;    -   a upper slip assembly and a lower slip assembly mounted on such        cylindrical tube and adapted to selectively engage the well        casing to anchor the pumpable seat assembly;    -   an elastomeric packing element mounted on said cylindrical tube        between the upper slip assembly and the lower slip assembly; and    -   a dissolvable ball having a sufficiently large enough outer        circumference so that it can sit on the ball seat and        temporarily restrict a flow of fluids to the portion of the        wellbore located below the pumpable seat assembly.

In one embodiment, the inner diameter of the cylindrical tube is greaterthan 1/4 inches. In another embodiment, the inner diameter of thecylindrical tube is greater than 1 inch. In another embodiment, theinner diameter of the cylindrical tube is greater than 2 inches. In oneembodiment, the cylindrical tube has at least one flow port located at alower end of the cylindrical tube.

Additional aspects and advantages of the present invention will beapparent in view of the description, which follows. It should beunderstood, however, that the detailed description and the specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of an exemplary embodimentwith reference to the accompanying simplified, diagrammatic,not-to-scale drawings:

FIG. 1 is a cross-sectional view of an exemplary embodiment of thepumpable seat assembly.

FIG. 2 is a partial cross-sectional perspective of a plurality ofpumpable seat assemblies set within a length of well casings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various embodiments of thepresent invention and is not intended to represent the only embodimentscontemplated by the inventor. The detailed description includes specificdetails for the purpose of providing a comprehensive understanding ofthe present invention. However, it will be apparent to those skilled inthe art that the present invention may be practised without thesespecific details.

The present invention relates generally to a process for fracturing,stimulating and producing a wellbore without having to mill out andremove fracturing/bridge plugs and to a pumpable seat assembly for usetherein.

FIG. 1 shows one embodiment of a pumpable seat assembly (10) useful inthe present invention, which assembly (10) is shown being set within awellbore casing (12). Pumpable seat assembly (10) comprises a generallycylindrical tube (14) having an upper end (15) and a lower end (17).Situated near the first end (15) of cylindrical tube (14) is an upperslip assembly (18) and situated near the lower end (17) of cylindricaltube (14) is a lower slip assembly (22). Both the upper and lower slipassemblies generally include a plurality of serrations (23) which engagethe casing (12) and prevent longitudinal movement of the slips (18) and(22) once set.

An elastomeric packer element (20) is mounted on the cylindrical tube(14) between the upper slip ((18) and the lower slip (22). The packingelement (20) is adapted to be deformed into sealing engagement with thecasing (12) upon compression of setting components (not shown). Althoughthe packing element (60) is shown and described as being one-piece it isto be understood that a packing element having multiple members iscontemplated under the present invention. In either case, the packingelement (20) is adapted to provide a fluid-tight seal between thecylindrical tube (14) and the casing (12).

The lower end (17) of the cylindrical tube (14) can further comprise oneor more flow ports (24). The flow ports (24) facilitate the flow of oilor gas from the region below the pumpable seat assembly (10) through thecylindrical tube (14) to the wellhead (not shown). The upper end (15)further comprises a time-dissolvable ball (28), which ball (28) is sizedto generally sit into and cover the seat (16) formed in the upperportion (15) of the cylindrical tube (14) to prevent the flow of fluidssuch as those used for fracturing, stimulating and the like from flowingthrough the cylindrical tube (14) to the formation below the pumpableseat assembly (10). The ball (28), however, is dissolvable within apredetermined passage of time to then allow the flow of oil and gas fromthe formation below to the surface. Thus, the dissolvable ball (28)functions to temporarily restrict the flow through the cylindrical tube(14) until it is desirable to do so. The inner diameter (ID) of thecylindrical tube must be large enough so that unrestricted flow canoccur therethrough. In one embodiment, the ID is about 2 inches but canbe larger, depending upon the ID of the varying casings and the toolsare run in therein.

An example of biodegradable balls that may be used in the presentinvention is BioBalls soluble ball sealers available from Santrol ofTexas. It is understood that other oil field service providers can alsosupply dissolvable products. Generally, dissolvable balls can includebiodegradable balls that can degrade over a period of hours or days whenexposed to a set of predetermined environmental conditions. For example,the environmental conditions can include normal wellbore operatingconditions of temperature and pressure at a particular depth orelevation in the wellbore, as well as the normal chemistry for drillingmud or pumping/frac fluids used during completion operations.

FIG. 2 shows an embodiment of a well completion process of the presentinvention using a plurality of pumpable seat assemblies (10) of thepresent invention. In FIG. 2, a horizontal portion of a well is shownwhich has been cased in with casing (12), such as steel pipe casing. Thecasing (12) may be cemented in place in the well. The horizontal wellportion in FIG. 2 comprises five separate producing zones, zone A, zoneB, zone C, zone D and zone E. The end of the casing (12) is shown aselement (130). The first zone to be fractured/stimulated would be thezone closest to the casing end (130), namely, zone A. A perforatingapparatus (not shown) can be used to form perforations 132 in the casing(12) and fracing/stimulating fluids can then be pumped down to completethe fracing/stimulating process.

The next producing zone to be perforated/fractured/stimulated would nowbe zone B. However, it is desirable that any fracing/stimulating fluidsthat are used to stimulate zone B do not reach zone A in order toprevent re-stimulating or re-fracturing an already stimulated/fracturedzone/interval. Thus, pumpable seat assembly (10 a) is pumped downholeand set just below zone B but above zone A. Dissolvable ball (28 a) isthen pumped down to cover the open seat of pumpable seat assembly (10a). This will then prevent any (racing/stimulating fluid from reachingzone A. After zone B is stimulated, the next zone to beperforated/fractured/stimulated is zone C, using a second pumpable seatassembly (10 b) which is pumped down the wellbore casing (12) followedby a second dissolvable ball (28 b). After zone C is stimulated, zone Dis the next producing zone to be perforated/fractured/stimulated usingpumpable seat assembly (10 c) and dissolvable ball (10 c). Finally,pumpable seat assembly (10 d) and dissolvable ball (10 d) is used whenzone E is perforated/fractured/stimulated.

From the foregoing description, one skilled in the art can easilyascertain the essential characteristics of this invention, and withoutdeparting from the spirit and scope thereof, can make various changesand modifications of the invention to adapt it to various usages andconditions. Thus, the present invention is not intended to be limited tothe embodiments shown herein, but is to be accorded the full scopeconsistent with the claims, wherein reference to an element in thesingular, such as by use of the article “a” or “an” is not intended tomean “one and only one” unless specifically so stated, but rather “oneor more”. All structural and functional equivalents to the elements ofthe various embodiments described throughout the disclosure that areknown or later come to be known to those of ordinary skill in the artare intended to be encompassed by the elements of the claims. Moreover,nothing disclosed herein is intended to be dedicated to the publicregardless of whether such disclosure is explicitly recited in theclaims.

What is claimed is:
 1. A process for fracturing, stimulating andproducing a wellbore having a plurality of oil or gas producing zones,comprising: introducing into the well a pumpable seat assemblycomprising a generally cylindrical tube having an outer diameter and aninner diameter with an upper end forming a ball seat; setting thepumpable seat assembly below an oil or gas producing zone to beproduced; introducing a dissolvable ball into the well, said dissolvableball having a sufficiently large enough outer circumference so that itcan sit on the ball seat and temporarily restrict a flow of fluids tothe portion of the wellbore located below the pumpable seat assembly;and fracturing the oil and gas producing zone to stimulate oil or gasproduction; whereby the biodegradable ball is configured to dissolvewithin a predetermined period of time so that when it dissolves any oilor gas produced from zones below the pumpable seat assembly can flowthrough the cylindrical tube.
 2. The process as claimed in claim 1,wherein the inner diameter of the generally cylindrical tube is about 1inch.
 3. The process as claimed in claim 1, wherein the inner diameterof the generally cylindrical tube is about 2 inches or greater.
 4. Theprocess as claimed in claim 1, wherein the inner diameter issufficiently large so that oil or gas can freely flow therethrough. 5.The assembly as claimed in claim 1, wherein the inner diameter of thegenerally cylindrical tube is between about 1 inch and 2 inches.
 6. Theprocess as claimed in claim 1, further comprising pumping a secondpumpable seat assembly comprising a generally cylindrical tube having anouter diameter and an inner diameter with an upper end forming a ballseat, setting the second pumpable seat assembly below a second oil orgas producing zone to be produced, and introducing a second dissolvableball into the well to restrict the flow from the previously formed oiland gas producing zone.
 7. A pumpable seat assembly for temporarilysealing a well casing, comprising: a generally cylindrical tube havingan outer diameter and an inner diameter with an upper end forming a ballseat; a upper slip assembly and a lower slip assembly mounted on suchcylindrical tube and adapted to selectively engage the well casing toanchor the pumpable seat assembly; an elastomeric packing elementmounted on said cylindrical tube between the upper slip assembly and thelower slip assembly; and a dissolvable ball having a sufficiently largeenough outer circumference so that it can sit on the ball seat andtemporarily restrict a flow of fluids to the portion of the wellborelocated below the pumpable seat assembly.
 8. The assembly as claimed inclaim 7, wherein the inner diameter of the generally cylindrical tube isabout 1 inch.
 9. The assembly as claimed in claim 7, wherein the innerdiameter of the generally cylindrical tube is about 2 inches or greater.10. The assembly as claimed in claim 7, wherein the inner diameter ofthe generally cylindrical tube is between about 1 inch and two inches.11. The process as claimed in claim 7, wherein the inner diameter issufficiently large so that oil or gas can freely flow therethrough.